1. Field
Example embodiments relate to a sense-amplifier, and more particularly, to a sense amplifier sensing and amplifying data on a pair of data line, a semiconductor memory device having thereof and a memory system having the semiconductor memory device.
2. Description of Related Art
In general, a semiconductor memory device like DRAM, SRAM includes a memory core, a data sense amplifier, and data output/input unit. The memory device outputs data to external device that stored at memory cells in the memory core through the data sense amplifier. As the memory device has been required to have more density, data line between the memory core and the data sense amplifier got longer and big load capacitance. So, most memory devices have a hierarchical data line structure, having a local data line and a global data line between the memory cell and the data sense amplifier. The local data line is a data line between bit line sense amplifier and a local sense amplifier. The global data line is a data line between the local sense amplifier and a global sense amplifier. The local sense amplifier is located inside the memory core. The global sense amplifier is located outside the memory device. So, the global data line is longer than the local data line in general
For read operation of the memory device, when the memory cell is selected, first data stored in the memory cell is sensed and amplified by the bit line sense amplifier and transferred to the local data line. Then data on the local data line is sensed and amplified by the local sense amplifier and transferred to the global data line. After that data on the global data line is sensed and amplified by the global sense amplifier and transferred to a data output unit. Finally the output data unit outputs data to an external device, like a memory controller.
There has been used two type of the global sense amplifier amplifying data on the global data line having small signal. Voltage-mode sense amplifier has low-power consumption but relatively low-speed operation. Current-mode sense amplifier has relatively high-speed operation but relatively high-power consumption.